Crystalline aggregates

The presence of hemoglohin-S (Hb-S) ia red blood cells leads to the formation of Hquid crystalline aggregates iaside the ceU under conditions of low oxygen tension (43,44). The morbid aggregates ultimately arrange themselves iato a gel-like material composed of long fibers that extend the entire length of the ceU and distort its usual shape. 

Polypropylene molecules repeatedly fold upon themselves to form lamellae, the sizes of which ate a function of the crystallisa tion conditions. Higher degrees of order are obtained upon formation of crystalline aggregates, or spheruHtes. The presence of a central crystallisation nucleus from which the lamellae radiate is clearly evident in these stmctures. Observations using cross-polarized light illustrates the characteristic Maltese cross model (Fig. 2b). The optical and mechanical properties ate a function of the size and number of spheruHtes and can be modified by nucleating agents. Crystallinity can also be inferred from thermal analysis (28) and density measurements (29). 

This starting material can be prepared as follows, 123 parts of finely powdered 6-amino-2,4-dimethylpyrimidine are suspended in 250 parts of dry pyridine and 222 parts of p-nitroben-zenesulfonyl chloride added at 50°C to 55°C. The whole is then warmed for 2 hours to 55°C, Water is added to the crystalline aggregate obtained, the precipitated bis-N-(p-nitrobenzene-sulfonyl)-6-amino-2,4-dimethylpyrimidine filtered off by suction and washed with water. It is purified by recrystallizing from methyl ethyl ketone. On slowly heating it decomposes on rapidly heating it melts at about 210°C to 215°C with decomposition. 

Characteristic of the microstructure of PET fibers in their final production form is the occurrence of three types of polymer phases crystalline, mesomorphous, and amorphous. The first phase is the result of crystalline aggregation of PET molecules, the second phase—of mesomorphous or, in other words, paracrys-talline aggregation, the third phase—of amorphous aggregation. The mesomorphous and amorphous phases together form a noncrystalline part of the fiber. 

A univocal confirmation of the development of crystalline aggregation in the fiber is the occurrence of layer reflexes Oil, HI, ill, and 101 on the textural x-ray diffraction pattern. The details of organization of the space lattice are defined by the parameters of the unit cell and the number of polymers felling into one cell. The data, established by different authors, are presented in Table 2. Daubenny and Bunn s [8] pioneer findings are considered the most probable for space lattices occurring in PET fibers. 

Specific carotenoid-protein complexes have been reported in plants and invertebrates (cyanobacteria, crustaceans, silkworms, etc.), while data on the existence of carotenoproteins in vertebrates are more limited. As alternatives for their water solubilization, carotenoids could use small cytosolic carrier vesicles." Carotenoids can also be present in very fine physical dispersions (or crystalline aggregates) in aqueous media of oranges, tomatoes, and carrots. Thus these physicochemical characteristics of carotenoids as well as those of other pigments are important issues for the understanding of their bioavailability. 

As a rule, the dispersed catalysts are polydisperse (i.e., contain crystallites and/or crystalline aggregates of different sizes and shapes). For particles of irregular shape, the concept of (linear) size is indehnite. For such a particle, the diameter d of a sphere of the same volume or number of metal atoms may serve as a measure of particle size. 

S. Yesslers, R. Boistelle, A. Delacourte, J. C. Guyot, and A. M. Guyot-Hermann, Influence of structure and size of crystalline aggregates on their compression ability, Drug Dev. Ind. Pharm., 18, 539 (1992). 

It is well known that many compounds are able to change their physical form whilst suspended in solution. For example, a compound of interest may change from one polymorphic form to another, while different crystalline aggregations of the same compound can have different solubility profiles. Impurities can mask the true solubility, and aggregation in solution can also change the thermodynamic equilibrium. Finally, errors which have been published in the literature data may in fact magnify from publication to publication. 

Solvothermal growth of single crystals or poly crystalline aggregates from hydro-thermal or ammonothermal solution. 

The experiments on alkali iodides, PEOx-Nal or PEOx-Lil [316-318] were performed on PEO chains of 23 or 182 (-CH2-CH2-O-) monomers and Orion ratios between 15 and 50. The incoherent scattering from protonated polymers was measured using INI 1C, which yields the intermediate scattering function of the self-correlation. The experiments were performed in the homogeneous liquid phase where the added salt is completely dissolved and no crystalline aggregates coexist with the solution, i.e. at temperatures around 70 °C. 

Pectolite [NaCa2Si30g(0H)] is found as white to translucent acicular radiating crystalline aggregates, often in association with the zeolite group of minerals, which are discussed later. In the crystal strucmre of pectolite, Csl and Na" occupy the sites between the single chains as described for pyroxenes. Chemical substitutions of Mn , Mg and Fe, for Na and Ca are common. The substitutions may be detected optically because they pro-... 

Variety names, such as chalcedony and jasper, are given to minute crystalline aggregates of low-temperature quartz. Those showing distinct banding pat-... 

The thiocyanate, [Rh en3](SCN)3, is formed from the iodide by treating it in aqueous solution with potassium thiocyanate. It separates in crystalline aggregates which always contain a little iodide. 

The appreciably lower micellar solubilities of oleic acid, oleyl alcohol, and propylene glycol monooleate are consistent with the view that the formation of a liquid crystalline aggregate—lamellar, cylindrical, or... 

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